1. Field of the Invention
The present invention relates to a method for generating character pattern data to display a character of an arbitrary size in an output device such as a printer, a display, etc. The present invention also relates to a method for making an image by scanning conversion in which picture subelements are provided as a scanning unit by dividing an original picture element and the interior of a contour line is colored by using the picture element having a gradation.
2. Description of the Related Art
In a work station, etc., there is a case in which an operator would like to display a character such as a Chinese character of an arbitrary size in an output device such as a display, a printer, etc. In a method for holding and displaying normal dot character pattern data, it is necessary to hold the dot character data very size as to output the character of plural sizes (e.g., 24.times.24, 32.times.32, 40.times.40, etc.).
However, for example, in the case of size 24.times.24, 72 byte per one character are required even in the case of a character having no gradation. Accordingly, when 7000 characters are held as a total of first and second kinds of Japanese JIS Chinese characters, a memory of 504 k byte is used. In the case of size 40.times.40, a memory of 1.4 M byte is used. Therefore, when the characters of various kinds of sizes are simultaneously held in dot font, a large amount of memory is required and therefore it is not economical so much.
Accordingly, there is a proposed technique in which the character of an arbitrary size is displayed in the output device from a dot character pattern of one size. For example, Japanese Patent Application Laying Open (KOKAI) No. 62-286753 discloses a technique for converting a dot character pattern of a large size having no gradation to a gradated character pattern of a small size on the basis of plural dots constituting the character pattern. By using this technique, it is also possible to increase the number of displayed characters as much as possible in the output device having low resolution.
However, when the dot character pattern of a large size is held and the above-mentioned character conversion is performed, a large amount of memory is also required and it is not economical.
As a method for holding the character pattern data by a small amount of used memory, there is a technique in which only a contour line of the character is held as character data and dot character patterns of various kinds of sizes are made from information of this contour line and are outputted to the output device having no gradation.
This method for making the dot character patterns from the information of the contour line is shown in the following literatures for example.
1. "Digital Formats for Typeface" Peter Karou, URW Verlag, 1987.
2. "CHARACTER GENERATION UNDER GRID CONSTR-AINTS", Roger D. Hersch, Computer Graphics, Volume 21, Number 4, July 1987, and
3. "Trial for making font for preview", Yoshio Ohno, Document processing and Human interface, 21-5, 1988/11.
Accordingly, when the character pattern data are held as the contour line, it is possible to hold the characters at a high grade by a small amount of used memory. Further, when an affine transformation provided by the following formula, ##EQU1## is performed, an arbitrary modification including enlargement and reduction in size can be provided. Accordingly, by using this nature, it is possible to make the pattern data of the character of an arbitrary size from one contour.
As mentioned above, when the character pattern data are held as information of the contour line, it is possible to make the pattern data of the character of an arbitrary size from this information of the contour line. Here, the arbitrary size simply means that in mathematics and various kinds of problems are caused when the data are outputted to the actual output device.
Therefore, the third literature mentioned above proposed a technique for making the thickness of horizontal and vertical lines equal to each other on the contour. However, in such a method, their thicknesses are compulsorily changed so that the original shape of the character tends to be changed and a slight change between character styles is especially canceled.
The above problems are caused in the case of the output device having a low resolution and an intermediate resolution about 300 dot/inch. Therefore, even when the contour data of character styles with high accuracy are provided, the output results provided by the output device having a resolution less than the intermediate resolution are lower in quality than those in the dot character pattern data and thereby cannot be used in an output equipment so much.
A method for improving the quality of an image by utilizing a picture element having a gradation is known as an anti-allasing method. In this method, there are two basic methods composed of a post filtering method and a prefiltering method.
The pre-filtering method is a method for removing an unnecessary component of an image made by one kind of digital low pass filter and displaying the image. In this method, the digital filter is made by utilizing a Fourier transformation, but the calculating amount thereof is a very large so that it takes much time to perform the calculation. Accordingly, it is difficult to apply this method to a coloring operation with respect to a region surrounded by an arbitrary contour line.
On the other hand, in the post filtering method, an original picture element (a physical picture element) in a device for outputting an image is divided into virtual small picture subelements to make the image having a resolution higher than the original resolution, thereby providing a desirous resolution by utilizing the gradation. In principle, this method is inferior to the pre-filtering method, but has the advantages that a portion surrounded by the arbitrary contour line can be also colored by a combination of this method and the scanning conversion method.
When the image is made by the scanning conversion to which such a post filtering method is applied, the subelements correspond to bits and a processing is performed as a block of picture subelements with respect to the original picture element. The number of bits "1" in each block is counted to provide the gradation of the picture element finally outputted. Therefore, in this method, there are many calculations of bit units and therefore it is difficult to perform the processing at a high speed.